Marginal bone loss in internal conical connection implants placed at the crestal and subcrestal levels before prosthetic loading: a randomized clinical study

Citation: Palacios-Garzón, N.; Mauri-Obradors, E.; Ayuso-Montero, R.; Velasco-Ortega, E.; Anglada-Cantarell, J.M.; López-López, J. Marginal Bone Loss in Internal Conical Connection Implants Placed at the Crestal and Subcrestal Levels before Prosthetic Loading: A Randomized Clinical Study. Materials 2022,15, 3729. https://doi.org/10.3390/ma 15103729 Academic Editor: Gherlone Felice Enrico Received: 8 April 2022 Accepted: 18 May 2022 Published: 23 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Marginal Bone Loss in Internal Conical Connection Implants Placed at the Crestal and Subcrestal Levels before Prosthetic Loading: A Randomized Clinical Study Natalia Palacios-Garzón1, Elisabeth Mauri-Obradors 1, Raúl Ayuso-Montero 2, Eugenio Velasco-Ortega 3, JoséMaría Anglada-Cantarell 2and JoséLópez-López 2,4,* 1 Faculty of Medicine and Health Sciences (Dentistry), University of Barcelona, 08907 L’Hospitalet de Llobregat, Spain; [email protected] (N.P.-G.); [email protected] (E.M.-O.) 2Oral Health and Masticatory System Group, Bellvitge Biomedical Research Institute IDIBELL, University of Barcelona, 08907 Barcelona, Spain; [email protected] (R.A.-M.); [email protected] (J.M.A.-C.) 3Department of Odontostomatology, Faculty of Dentistry, University of Seville, 41009 Seville, Spain; [email protected] 4Service of the Medical-Surgical Area of Dentistry Hospital, University of Barcelona, 08907 Barcelona, Spain *Correspondence: [email protected] Abstract: The vertical position concerning the bone in which the implants are placed has been related as one of the factors causing marginal bone loss. The objective of this study was to evaluate the bone loss that occurs before prosthetic loading around tapered internal connection (CIC) implants placed at the crestal (C) and subcrestal (S) levels. Method: A randomized clinical trial (RCT) was carried out, with a sample size of 62 implants placed in 27 patients who underwent radiological controls on the day of placement, at one month, and at 4 months, and stability was measured by resonance frequency analysis (RFA) on three occasions. Results: Bone loss in implants C and S from the time of placement (T0) and the month after (T1) was not significant (p= 0.54) (C = 0.19 mm and S = 0.15 mm). The difference between one month (T1) and four months (T2) (C = 0.17 mm and S = 0.22 mm) was not significant either (p= 0.26). The difference between the day of placement (T0) and the third and last measurement (T2) was almost null (p= 0.94) (C = 0.35 mm and S = 0.36). The overall success rate of the implants was 97.8%. The stability of the implants measured with RFA went from 70.60 (T0) to 73.16 (T1) and 74.52 (T2). Conclusions: No significant differences were found in the bone loss for implants placed at the C and S levels. The millimeters of bone loss detected in both vertical positions did not have a significant impact on the stability of the implants. Keywords: external connection; internal connection; peri-implant bone loss; bone remodeling; preload prosthesis 1. Introduction One of the challenges of current research in implantology is to reduce the minimal bone loss that occurs in the most coronal area of the implant, and that is more accentuated during the first year [1]. According to the standards of optimal conditions that implants must meet, it is said that they must be surrounded by a specific quantity (minimum 2mm)of quality bone at the morphological level [ 2 ]. This parameter is difficult to comply with within the vestibular area; here, we find a type of bone that, when there are teeth, can measure 1 mm or less. The vestibular bone is especially sensitive to the changes produced by the surgical act that occurs when the extraction and placement of the implant are performed [ 3 ]. Taking into account the particularity of this bone, a subcrestal implant placement approach could be favorable if we take into account that the preservation of this crestal bone can provide us with the stability of our soft tissues, a crucial element for the success and aesthetics of our treatment [4]. Materials 2022,15, 3729. https://doi.org/10.3390/ma15103729 https://www.mdpi.com/journal/materials Materials 2022,15, 3729 2 of 15 It has been suggested that a subcrestal implant placement may favor marginal bone preservation [ 5 ]. This concept is not current; it dates back to the 1960s, when the promoter of implantology, Dr. Branermark, already recommended it as one of his criteria for the success of implants, stating that burying the implant was necessary so that it would not be exposed after the bone remodeling process occurs [6]. This fact continues to be much discussed today. According to the latest studies collected in a systematic review and meta-analysis where only this aspect was assessed as the cause of bone loss, we can see that the literature is not clear enough. On the one hand, some authors defend the subcrestal placement of the implants, arguing the good results of its use. Especially in aesthetic areas, these studies affirm that the fact of deepening the implant would help to have a better emergence profile [ 7 ], preventing the implant surface from being exposed in the long term, thus reducing the probability of suffering from peri-implantitis [ 8 , 9 ]. On the other hand, the authors who defend a crestal position of the implant obtained evidence that demonstrates an increase in bone loss when the implant is buried. This loss could be due to bacterial colonization in the junction area between the implant and the abutment which, being deep, could be ideal for the proliferation of anaerobic bacteria [10–12]. The present work focuses on analyzing the bone loss that occurs due to the vertical position concerning the bone in which the implant is placed. However, many factors cause this loss; among these, we find the type of connection [ 13 ], surface [ 14 ], bone remodeling [ 15 ], occlusal load [ 16 ], mechanical imbalances [ 17 ], and bacterial infiltration [ 18 ]. Bone loss can be due to several factors that can be present at the same time, and it is difficult to isolate just one of them to assess it more precisely. Taking these limitations into account, in this clinical study, an attempt was made to control all the parameters that could affect bone loss as much as possible. Both positions of the implants had the same connection, macro design, and type of surface in the body of the implant; the closure abutment was placed in all of them, and the second phase was performed at a later time. Bone loss was analyzed before prosthetic loading. 2. Materials and Methods 2.1. Study Population A randomized clinical study was carried out at the University of Barcelona Dental Hospital. This was approved by the ethics committee CEIC HOUB (Comitèd’Etica i InvestigacióClínica de l’Hospital Odontològic Universitat de Barcelona) on 5 May 2017, with approval code 648. The criteria of the CONSORT guidelines for conducting clinical trials were taken into account, and they were included in the clinical trials database ClinicalTrials.gov ID: NCT03232372. The patients had to present total or partial edentulism in the mandible and/or maxilla, with at least 2 dental absences in the same maxilla. It was established that the implants should be placed in areas where there was adequate bone volume so that no threads would be exposed during surgery. In this way, the use of biomaterials was avoided in an attempt to reduce bias. In all cases, a diagnostic CBCT was performed to ensure that the area where the implants were to be placed had sufficient bone volume. It was established that a minimum height of 8 mm and a bone width >7 mm were allowed, except for the anterior sector, where, due to bone limitations [ 17 ], a width of 5–6 mm was allowed. Teeth should have been extracted at least 4–6 months before implant placement. Patients with serious systemic diseases, such as recent heart attack, coagulation disorders, cancer, uncontrolled diabetes, psychiatric contraindications, and active infection, as well as pregnant or lactating women, were excluded. Patients with pharmacological treatments capable of affecting bone healing (Bisphosphonates) and gingival health, such as some anticonvulsants (Phenytoin), immunosuppressants (Cyclosporin A), and calcium channel blockers (Nifedipine, Verapamil, and Diltiazem), were also excluded. All patients received instructions to improve their oral hygiene prior to the implants’ placement. An intraoral examination took place where previous dental treatments, dental Materials 2022,15, 3729 3 of 15 absences, plaque index, probing, mesial and distal contact of the area to be implanted, and type of teeth or opposing prosthesis were recorded. 2.2. Study Design and Randomization Before the surgery, the researcher (NPG) performed the randomization and assignment of the implants into two groups: A, the subcrestal group; and B, the crestal group. With this purpose, an application generating random numbers was used (Random Numbers— Version 4.2, 2015). Taking into account research that deals with the design and analysis of studies of split mouths, it was decided that patients had to have at least two edentulous spaces in the same jaw [ 19 ]. Thus, on the basis that the ossification of the mandible and the maxilla are different from each other [ 20 ], this could reduce the bias when comparing bone loss. In order to calculate the sample size required to test the hypothesis on the difference in bone loss of implants placed at the crestal and subcrestal levels, the following formula was used: n=2Zα+Zβ2×S2 d2 where nis the subjects in each of the two groups (crestal vs. subcrestal); Z α is the Z-value correspondent to the accepted possible risk of mistakenly rejecting a true null hypothesis; Z β is the Z-value correspondent to the accepted possible risk of failing to reject a false null hypothesis; Sis the standard deviation in mm of bone loss in implants placed at crestal and subcrestal levels; and dis the minimum desired value in mm of the difference in bone loss between the two groups. After carefully reviewing the related literature [ 9 , 21 , 22 ], it was found that the average standard deviation of bone loss for implants placed at crestal level was approximately 0.35 mm, while, to obtain a significant difference with implant placed at subcrestal level, it would be required to achieve a difference in bone loss of approximately 0.28–0.30 mm. Following the standard procedure, to detect possible differences between treatments, we accepted a risk of 5% and a statistical power of 95. Considering the fact that a recent systematic review [ 23 ] on the difference of bone loss between crestal and subcrestal placements reported non-significant differences between the two positions, in this study, we decided to perform two-tailed hypothesis testing. After all of these considerations and by applying the above specified formula, it was found that a minimum of 28 observation for each group would be required. After performing the randomization between treatments, 29 implants were placed at the crestal level, while 33 implants were placed at the subcrestal level. Randomization was performed between three groups because we wanted to compare the internal and external connections. However, for the study reported in this article, bone loss in implants placed at the crestal and subcrestal levels was analyzed only at the conical internal connection. This decision, taken to avoid the risk of a possible interaction between connection and implant position, implies that the sample size is smaller and equal to 29 in internal connection crestal implants and 33 in internal connection subcrestal implants. 2.3. Types of Implants The implants belonged to ETK ® manufacturing (Barcelona, Spain), Naturactis ® , and Naturall ® . All implants were platform switching and had the same surface type: titanium oxide sandblasting and etching with nitric and hydrofluoric acid from the apex to the neck of the implant. The Naturactis ® implant, designed for subcrestal placement, consisted of the entire surface treated to promote bone formation on the entire surface of the implant neck. The Naturall ® implant designed for juxtacrestal positioning had a machined surface on the implant neck, with a micro-groove of 0.2 µ m Ra for better mucosal adherence. (Figure 1). Materials 2022,15, 3729 4 of 15 Materials 2022, 15, x FOR PEER REVIEW 4 of 16 2.3. Types of Implants The implants belonged to ETK® manufacturing (Barcelona, Spain), Naturactis®, and Naturall®. All implants were platform switching and had the same surface type: titanium oxide sandblasting and etching with nitric and hydrofluoric acid from the apex to the neck of the implant. The Naturactis® implant, designed for subcrestal placement, consisted of the entire surface treated to promote bone formation on the entire surface of the implant neck. The Naturall® implant designed for juxtacrestal positioning had a machined surface on the implant neck, with a micro-groove of 0.2 μm Ra for better mucosal adherence. (Figure 1). Figure 1. Images of implants placed at the subcrestal (A) and crestal (B) levels. The drilling sequence was carried out according to the instructions of the implant brand regarding bone quality. For placing all the implants, the motor was programmed at 32 rpm and 35 Ncm. 2.4. Surgical Intervention and Clinical Follow-Up Before surgery, all patients underwent a 0.2% chlorhexidine rinse (Bexident Post® ISDIN SL., Barcelona, Spain); this protocol was carried out to reduce the bacterial load, since chlorhexidine, thanks to its bactericidal and bacteriostatic effects, would help us prevent the post-surgical infection [24]. The anesthesia used was 4% articaine with 1:100,000 epinephrine (Inibsa®, Lliça de Vall, Barcelona, Spain). We made a crestal incision and raised a full-thickness flap. The implants were placed by students in the 3rd year of the master’s degree in Medicine, Surgery, and Oral Implantology at the University of Barcelona, always with complete subordination. In this way, the same protocol was strictly followed, and we avoided the results obtained depending on the possible experience and/or preference of the operator. The entire procedure was supervised by NPG and JLL. Regarding the healing period, in the implants placed in the mandible, 3 months were waited before performing the second phase and 4 months in the maxilla. 2.5. Radiographic Monitoring of Bone Loss Standardized orthopantomography was performed. X-ray acquisition times were at the time of implant placement (T0), one month after implant placement (T1), and 3–4 months (T2). For better reproducibility, all measurements made on the radiographs were made by one examiner (NPG), and none of the implant placement surgeries were performed by the examiner (NPG). In addition, the patients were unaware of the position in which each type of implant was placed, so we can say that this is a single-blind study. Measurements were made by using Planmeca Romexis® software to process 2D images generated by the X-ray units. The calibration tool ensured that the measurement was correctly performed, given that it takes into account the length of each implant. Since all A B Figure 1. Images of implants placed at the subcrestal (A) and crestal (B) levels. The drilling sequence was carried out according to the instructions of the implant brand regarding bone quality. For placing all the implants, the motor was programmed at 32 rpm and 35 Ncm. 2.4. Surgical Intervention and Clinical Follow-Up Before surgery, all patients underwent a 0.2% chlorhexidine rinse (Bexident Post ® ISDIN SL., Barcelona, Spain); this protocol was carried out to reduce the bacterial load, since chlorhexidine, thanks to its bactericidal and bacteriostatic effects, would help us prevent the post-surgical infection [24]. The anesthesia used was 4% articaine with 1:100,000 epinephrine (Inibsa ® , Lliça de Vall, Barcelona, Spain). We made a crestal incision and raised a full-thickness flap. The implants were placed by students in the 3rd year of the master’s degree in Medicine, Surgery, and Oral Implantology at the University of Barcelona, always with complete subordination. In this way, the same protocol was strictly followed, and we avoided the results obtained depending on the possible experience and/or preference of the operator. The entire procedure was supervised by NPG and JLL. Regarding the healing period, in the implants placed in the mandible, 3 months were waited before performing the second phase and 4 months in the maxilla. 2.5. Radiographic Monitoring of Bone Loss Standardized orthopantomography was performed. X-ray acquisition times were at the time of implant placement (T0), one month after implant placement (T1), and 3–4 months (T2). For better reproducibility, all measurements made on the radiographs were made by one examiner (NPG), and none of the implant placement surgeries were performed by the examiner (NPG). In addition, the patients were unaware of the position in which each type of implant was placed, so we can say that this is a single-blind study. Measurements were made by using Planmeca Romexis ® software to process 2D images generated by the X-ray units. The calibration tool ensured that the measurement was correctly performed, given that it takes into account the length of each implant. Since all patients were required to have a CBCT before surgery, it was decided not to perform conebeam radiographs to limit multiple radiation exposures. To carry out the measurements, two points were marked on the implant platform that, when joined horizontally, represented zero height. Perpendicular to this line, two straight lines were drawn mesial and distal to the implant until contact with the bone. If the implant was coronal to the bone, the result would be interpreted as negative, whereas, if the implant was infracrestal, the result would be positive. The difference between the mean of the mesial and distal measurements at different times was used to calculate the bone loss in the orthopantomography (Figure 2). Materials 2022,15, 3729 5 of 15 Materials 2022, 15, x FOR PEER REVIEW 5 of 16 patients were required to have a CBCT before surgery, it was decided not to perform conebeam radiographs to limit multiple radiation exposures. To carry out the measurements, two points were marked on the implant platform that, when joined horizontally, represented zero height. Perpendicular to this line, two straight lines were drawn mesial and distal to the implant until contact with the bone. If the implant was coronal to the bone, the result would be interpreted as negative, whereas, if the implant was infracrestal, the result would be positive. The difference between the mean of the mesial and distal measurements at different times was used to calculate the bone loss in the orthopantomography (Figure 2). (A) Figure 2. Cont. Materials 2022,15, 3729 6 of 15 Materials 2022, 15, x FOR PEER REVIEW 6 of 16 (B) (C) Figure 2. Measurement of peri-implant bone loss: (A) after implant placement, (B) after 1 month, and (C) after 4 months. Figure 2. Measurement of peri-implant bone loss: ( A ) after implant placement, ( B ) after 1 month, and (C) after 4 months. Materials 2022,15, 3729 7 of 15 2.6. Resonance Frequency Analysis (RFA) Implant stability measurements were performed by using RFA with the Penguin RFA ® device (Penguin RFA, Klockner Barcelona, Spain) in three moments. The measurement times were the day of implant placement, when the healing abutment was placed (second phase), and before the placement of the prosthesis. Two measurements were made for each implant: one vestibular–palatal from the buccal side and one mesiodistal from the mesial side. The recording times were decided according to the study carried out by Pozzi et al. in 2014 [25]. 2.7. Statistical Analysis The data collected were processed by using the statistical package STATA 14.0. A descriptive analysis of the qualitative and quantitative variables was performed. The relationship between bone loss and implant position was analyzed by using the parametric t-test. The level of statistical significance chosen was 5% (α= 0.05). To evaluate the association between the dependent variable, bone loss from T0 to T2, and the independent variables, placement C or placement S, a multiple linear regression analysis was used. All the variables that were considered to potentially affect the relationship of the study, such as sex, age, and smoker, were used as control variables in the regression, as well as the number of cigarettes per day, maxillary type, ISQ (implant stability quota), and mesial and distal implant contact. 3. Results 3.1. Patient Data A total of 27 patients (12 women and 15 men) with an average age of 56 years, an average height of 1.67 m, and an average weight of 75 kg participated in this study. There were no dropouts. Regarding brushing frequency, 19% of the patients reported brushing their teeth 2 or 3 times a day, 67% 1 or 2 times a day, and 15% not once a day. According to the classification of periodontal diseases taken from the World Workshop in 1989 [ 26 ], five patients had gingivitis associated with dental plaque, four patients had generalized chronic periodontitis, and one patient localized chronic periodontitis. Periodontitis is a disease that contributes to the loss of the supporting tissue of teeth and implants. Patients with generalized periodontitis would continue to undergo plaque control of the disease and, if necessary, a treatment based on the elimination of bacterial deposits that adhere to the surface of the tooth and the implant, accompanied by antimicrobial therapy [ 24 ]. The control visits would be carried out every 6 months in the periodontics service, where, in addition to the conventional treatment, in many cases, diode laser treatments are carried out, since it has been seen that they are very effective in reducing anaerobic microorganisms that inhabit the pockets [ 27 ]. A total of 26% were smokers (four women and three men), of whom two smoked more than 20 cigarettes a day, one patient between 11 and 15 cigarettes a day, three patients between 6 and 10, and one patient less than 5 cigarettes a day. A total of 89% had partial edentulism and 11% total edentulism (Table 1). Materials 2022,15, 3729 8 of 15 Table 1. General patient data. General Patient Data Total Sex Women 12 Male 15 Average age 56 years Average height 1.67 m Middle weight 75 kg Number of cigarettes per day 1–5 1 patient 6–10 3 patients 11–15 1 patient 16–20 0 patients ≥20 2 patients Smoker No 20 patients; 74% Si 7 patients; 26% Periodontal diseases Gingivitis 5 patients Generalized chronic periodontitis 4 patients Localized chronic periodontitis 1 patient Edentulism Partial 24 patients 89% Total 3 patients 11% Brushing frequency 0 times a day 4 patients 15% 1 or 2 times a day 18 patients 67% 3 or more times a day 5 patients 19% 3.2. General Data of the Implants Sixty-two implants were placed (33 designed for infracrestal placement and 29 crestal). During surgery, there were no complications such as fenestrations or dehiscences, and complete closure of the wound without tension was achieved in all cases. One implant was mobile at the time of the second phase and was explanted, obtaining a survival rate of 98.4%. Most of the patients would be rehabilitated with single crowns and fixed prostheses. These prostheses were made by using CAD-CAM technology to ensure better passivity and control of distortion that can occur when performing procedures such as casting. Although monolithic zirconia would have been a favorable material due to its aesthetics, resistance, and less plaque accumulation, the material of choice in this study was conventional metal–ceramic [28]. In the case of totally edentulous patients, these would be rehabilitated with overdentures on Locators®(Table 2). Table 2. General implant data. General Implant Data Total 62 implants Maxilla 40% Mandible 60% At the molar level 50% At the level of premolars 34% At the incisor level 16% 27 patients 24 patients Crowns and bridges 3 patients Overdentures Materials 2022,15, 3729 9 of 15 3.3. Bone Loss The first comparison indicates an average bone loss of 0.19 mm for crestal implants and 0.15 mm for subcrestal implants. The said loss was found between the first and the second measurement. The test returned a t= 0.61, with a value of p= 0.54 (Table 3and Figure 3). Table 3. Bone loss in crestal and subcrestal implants. T0–T1 Average SD 95% CI C 0.19 0.39 (0.04–0.34) S 0.15 0.14 (0.1–0.19) t-test 0.61 p-value 0.54 C, crestal; S, subcrestal; SD, standard deviation; CI, confidence interval; T0, day of implant placement; T1, one month after placement. Materials 2022, 15, x FOR PEER REVIEW 9 of 16 Table 3. Bone loss in crestal and subcrestal implants. T0–T1 Average SD 95% CI C 0.19 0.39 (0.04–0.34) S 0.15 0.14 (0.1–0.19) t-test 0.61 p-value 0.54 C, crestal; S, subcrestal; SD, standard deviation; CI, confidence interval; T0, day of implant placement; T1, one month after placement. Figure 3. Bone loss (mm) in crestal vs. subcrestal implants between the first and second measurement (T0–T1). Bone loss of 0.19 mm for crestal implants and 0.15 mm for subcrestal implants. The second comparison considers bone loss between the second and third measurements. The mean is 0.17 mm for the crestal placement and 0.22 mm for the subcrestal placement. The test returned us a t = −1.13, with a p = 0.26 (Table 4 and Figure 4). Table 4. Bone loss in crestal and subcrestal implants. T1–T2 Average SD 95% CI C 0.17 0.20 (0.08–0.24) S 0.22 0.14 (0.17–0.26) t-test −1.13 p-value 0.26 C, crestal; S, subcrestal; SD, standard deviation; CI, confidence interval; T1, one month after placement; T2, prosthetic restoration Figure 3. Bone loss (mm) in crestal vs. subcrestal implants between the first and second measurement (T0–T1). Bone loss of 0.19 mm for crestal implants and 0.15 mm for subcrestal implants. The second comparison considers bone loss between the second and third measurements. The mean is 0.17 mm for the crestal placement and 0.22 mm for the subcrestal placement. The test returned us a t = −1.13, with a p= 0.26 (Table 4and Figure 4).